To make it easier to narrow it down to three, I'm going to interpret favorite as "vids I watched obsessively in 2013".
charmax's Devotion (Xena: Warrior Princess; Xena/Gabrielle)
MY FEELS ALL OVER THE SCREEN LET ME SHOW YOU THEM. This is a beautifully made vid that has made it impossible to not think "Xena" when I hear Amy Ray sing, and "Gabrielle" when I hear Emily Sailers. I probably watched this, teary-eyed and all, every day for like a month after finishing Xena. Because basically I was like OMG OTP I FINALLY UNDERSTAND SHIPPING IS THIS HOW FANNISHNESS FEELS TO OTHER PEOPLE?
Alas, this was the only Xena vid I could find that really resonated with my love of this pairing. Which is part of why I had to make another one. :D
chaila's Keep the Streets Empty For Me (Twilight; Bella/Vampirism)
I don't think I've ever seen a vid that so fundamentally changed the way I thought about a source before. And I've never watched a vid on repeat that wasn't one of my main fandoms, except this one. First off, I love the use of Bella's eyes and her gaze. I love how often she's just LOOKING, WATCHING, so intently. There are a few moments where she's looking at Edward and he's looking back and I expect her to look away and SHE DOESN'T. I LOVE THAT. The use of text, illustrations, and nature imagery in the vid is also fantastic. It's a really effective way to convey the message without feeling even slightly anvilicious. Plus the editing and musicality is super pretty and well-done, but what really excites me about this vid is that those qualities aren't just ends in themselves: they're used to make a super interesting point. And it makes that point so well.
shati's Boulevard of (Buffy the Vampire Slayer; Slayer Ensemble)
My favorite Buffy vids are the ones that explore what it means to be a Slayer, and I love this one's emphasis on relationships between slayers. I almost die of happiness at the second "my shadow's the only one that walks beside me", which completely reinterprets that line just like ( a spoilery thing that happened ). (Also can be interpreted as a femslash vid, though I don't think of it that way.)
Lately I have become totally obsessed with the editing techniques shati uses, especially the intercutting and repeated returns to the same or similar clips throughout the vid. It's super effective at drawing out themes that connect different characters, and showing how they change over the course of the series. The really frequent intercutting between a few different scenes -- e.g., the Kendra section that intercuts between Kendra & Buffy NotHugging and ( a spoilery thing that happened ) -- are really powerful, and so different from my own vidding style. I LOVE it, and I've been studying it a lot lately and trying to figure out exactly how it works so I can STEAL IT.
I still have plenty of days left if anyone wants to prompt me.